Photometer



Feb. 9 1926.

H. LUX

PHOTOMETER Filed May 1, 1924 JBZ/enfor- Patented Feb. 9, 1926.

UNITED STATES HEINRICH LUX, or BERLIN, GERMANY.

PHOTOMETER.

Application filed May 1,

To (di fai/ioni fait may concer-n.'

.Be it known that I, HnrNmcH LUX, a citi- .zen or" Germany, and a resident of Berlin, Germany, have invented new and useful Improvements in Photometers, of which the :following is a specification.

The present invention relates to photo -'meters and has 'tor its objectto provide a photo'n'ieter by means of which the brightness (h'iminous density) of surfaces which radiate light or reflect light, can be directly ascertained without the necessity of comparing said surface with a light-source of i-nown candle power. Owing to this fact I have been able to provide a photometer i which can be readily applied for measuring quickly and, sufficiently accurate the illumination, for instance, of working places, dwelling rooms, cellars, storing rooms, etc., as well as the candle power of light sources, such for instance, as the head lights orn power cars, and the like. My invention is based on the well-known intern ference phenomenon obtained by superpos- 'ing two transparent plates having parallel lines ruledpthereon, and turning said plates so that said ruled lines cross" each other. According' to the angle under which the parallel Klines intersect one another, the crossing points form -lines Aor bands of smaller or thicker widths. The smaller the angle is, the thicker appear these secondary lines, and vice versa. Now, if the surface the brightness of which is to vbe measured, is 'relatively dark, the lined plates need only to be turned slightly to render those secondary bands or lines as invisible to a normal eye. It isknown that visual signs, such, for instance, as iine lines, small printed letters, and the like, can be perceived the `more distinctly, the better they are illuminated or the stronger their brightness is. In the case oi the brightness being comparatively slight,the visual signs must be thicker or larger than if the brightness is comparatively strong. Iteversely, that slighter or stronger lineness of the visual signs which can just be perceived can be used as a measure for ascertaining the existing brightness or illumination. other o t.' the two pla'tes having parallel lines ruled is turned, there then arise if the angle of turning is small a few and strong secondary lines; if the turning is continued, the secondary lines become finer and hner and can, hnally, be perceived as nomenon obtained by the groove a.

Now, if one or theV 1924. serial No. 710,441.-

visual signs only if the strength of the brightness or illumination is increased correspondingly. It' a distinct brightness or illuminationexists Vwhich is to be judged ot', one of the ruled plates must be turned @which I will now describe with reference to the drawings forming a part of this application, and illustrating by way of` example an embodiment of my invention.

Fig. l is a vertical section, and

Fig. 2a side view of the object-end of thc photometer. Y

Figs. 3 and l show plates having parallel lines ruled thereon.

Fig. 5 killustrates the interference phesuperposing said plates so that the ruled lines thereon cross each other.

Figs. 6 and 7 illustrate, in a plan and side view, respectively, a goniometer device applied to the objecteend of the photometer s iown'in Figures l and 2.

The photometer illustrated comprises two telescopically arranged tubes t t1 of which t1 is provided with an ond wall p having a contracted sight hole corresponding with another sight hole provided in a diaphragm B arranged at a distance from said end wall y). The tube t1 can be telescopically moved within the tube t in order to adjust the instrument to thatrange of vision at which the secondary lines can be clearly distinguished. To the tube 1s aiiixed an annular Amember having a circumferential groove that its outer surface lies flush with the outer surface of the annular member An- ;other plate r1 is mounted in another annular member a revolubly attached to the member and coupled therewith by pins al engaging Both plates r1 and r2 are provided with ruled lines as shown in Figures 3 and 4.

j provided on the member a and co-operating with a mark 'il of the member b. Figure 5 illustrates roughly the appearance of the secondary lines when the superposed plates rl, have been turned relatively to one another. y

Since within those degrees of brigl'itness which come into regard with respect to good seeing, and which lie between l() Millilambert to l Lambert, the visual acuity Otall normal eyes shows only very slight ditferences, the latter may beneglected, with out thereby pereeptibly .fil'lecting the aecuracy ot my new photometer for all practical purposes.

l gauge 'the graduation scale 'illy means el a plurality ol sur faces the light' emitting power oi whicl'i isaccurately known.

liner "aduation can be obtained by enlarging the are of the' scale, as Afor instance, by means of fran'ie legs s' and si which are secured tothe annular member a by means of an angle piece 7a.. Theflatter isprovided with a' pin g on which is rev"- olubl;T n'iounte'd a pinion ,t engaging a curved rack @secured vto the annular meinber a. To the pinion is lixedlysecured a pointer co-operatinp` with a scale fig. ny angular turn between the members a and b is indicated considerably enlarged on the scale 2 by the pointer i v l am aware thatV any other gon'iometer device maybe used in combination withy n iy new photometcr, so" l do not limit my claim to any constructive` particulars illustra-ted in the drawings. The mode oE usingmy newV photometer isa's follows. Before l view the surface or lamp the lcandle power of which l desire to determine, I adjust the tubular length ot the apparatus to thevisual acuity of my eye by con'strueting` or extend'- ingthe telescopical tubes t and' t1 until ,I clearly distinguish the lines ruled' onplate r2 which lines cover the corresponding lines on plate r1 when the scale z' (1n Fig.V 2), or 2 (in Fig'. G) indicates a small ditlerencevfrom the Zero position, Having thus adjusted the photometer I view through it the surl'acc or light source to be measured and slowly turn the members a and b relatively to each other .until the secondary lines or bands appearing on said plates 712, r1 grow taint and finally become invisible within the light viewed. The candle power of this lightmay then be asccrtainedtrom the position' ot the mark l (in Fig@ 2) or the pointer (in Figure 6). As a matter of tact I may follow the opposite course in gauging Ithe scale by xingthe Zero position at` that angular relativeposition otthe plates r1 and r2 wherein the secondary lines are iuvisibleand then vary this angle until said secondary lines become clearly distinguishable. -i What' l claim and desire to secure by Letters Patent of the United States is 11A photometer, comprising, in combination, a pair ot superposed transparent plates sach having parallel lines ruled thereon, means tor tui-nine said plates relatively to each other,'a scale indicating the variable relative angular position between said plates, saidscale being ranged so that each scale mark indicates a'. `sted brightness.

2; A photometer, con'iprising, in combination, a pair of superposed transparent plates having` parallel vlines ruled thereon, means for turning said plates relatively to each other, a scale indicating the variable relative angular positions between said plates, said scale being` gauged sothat each scale ina-rk indicates a tested brigl1tness ,fand a hollowstructure axially extending the space in' front of one tot said plates and adapted to assist the human eye in examining any variation in the thickness of the secondary lines appearing` when said respective lines onl said platescross each other. e 7 8. A; photometer,` comprising, in combina tion, a pair of superposed transparent plates eacll having parallelV lines ruled thereon,

means for turning said plates relatively to each other, a graduated member adapted to ind'cate the variable angular relative posi* rtiens between said plates, said scalev being 'gauge-d' so that' each scale mark indicates a tested brightness, and a goniometer device combined Iwith said plates and adapted to render anyfvariation in the relative Vangular 'position between said plates perceptible.

4. AY photometer, comprising, in combination, a pair of' superposcd transparent plates each hai/'ing parallel lines n ruled'` thereon,

means 'or turning said plates relatively to cach other, a scale indicating the variable angular relative positions between said plates, said scale being` gauged so that each scale mark indicates a tested brightness, 'a hollow structure axially extending the space in front otone of lsaid plates and adapted to assist the human eye in examining,- any variation in the thickness of the secondary lines appearing` when said linesonr said plates ycross eachother, and a goniorneter ydeviceadapted to render a variation in the angular relative positions between said plates perceptible.

` DR. HEINRICH LUX, 

